1. Field of the Invention
This invention pertains to devices used in connection with the detection and measurement of the electrical environment of buried metallic pipelines which become subject to the destructive effects of corrosion. More specifically, the present invention pertains to an electrolysis test station terminal assembly which provides insulation, protection and support for conductive wires coupled to the underground pipe and reference electrodes or ground contacts, and is positioned by means of the subject invention to an above-ground orientation in plain view and with exposed terminal leads for direct measurement.
2. Prior Art
The corrosive destruction of expensive underground pipe systems continues to create serious problems for virtually all industries utilizing underground conduit. For example, the telephone industry, power and light industry, gas and oil industry, and many other similar industries rely heavily on buried pipelines to convey and protect fuels, cables, and other materials. In view of the substantial expense related to underground pipeline construction and subsequent repair efforts where such pipeline is damaged, continuous attention has been applied to reduce and detect corrosion activity.
Although corrosion may result from numerous types of chemical reactions and environments, buried metallic pipelines are particularly subject to electrochemical corrosion. Two specific categories of electrochemical corrosion include (i) galvanic and (ii) straight current corrosion. In the case of galvanic corrosion, a current flow is established between discrete areas of oxidation and reduction reactions at the buried pipeline. Such galvanic currents are the effect of corrosion activity and provide means for electrical detection of corrosion by current measurement. A common source of galvanic corrosion occurs when a differential aeration corrosion cell is established on the metallic surface of an underground pipe in contact with an electrolyte.
In addition to development of current by reason of oxidation reduction reactions in the corrosion process, current may also develop from stray sources foreign to the affected pipeline. Such stray currents unusually occur in metropolitan environments where intense earth voltage gradients may exist, such as from a direct-current railway system or nearby impressed current cathodic protection anode bed. The underground pipe surface receiving current where the earth voltage is more positive is protected from corrosion. On the other hand, if earth voltage is less positive, the metallic surface acts as an anode and is subject to corrosion reaction.
Prior art methods of solving the corrosion problem resulting from electrochemical causes have included treatment of the cause as well as the effect of the reaction. Solutions have included coating the metallic pipes with insulative materials which operate as a barrier to current flow. Other protective coatings are utilized to establish an insulative barrier between electrolyte within the underground soil and the metallic surface of the pipe. Such coatings range from coal tar enamel coatings, asbestos felt, and polymer coatings.
In addition to protective coatings, sacrificial anodes may be buried for purposes of preferential reaction by reason of stray current which could otherwise attack the metallic substance of the buried pipe. Pieces of magnesium, for example, may be buried under the earth at underground sites which are likely to present likelihood of corrosive attack.
It will be apparent that ongoing measurement of current and/or voltage in the pipe vicinity is required to verify that the protective coatings over pipe surfaces or adjacent sacrificial anodes are properly operating. For example, the presence of galvanic current near the surface of a coated pipe would indicate corrosive action and a likely break in the coating material. Similarly, a change in current flow in an environment with a sacrificial anode can indicate changed conditions which would require other preventive action.
Accordingly, it has been well-known to implace test leads at the pipe surface, ground potential sites, or other underground electrical points of interest and to maintain a program of periodic measurement of current or voltage potential in order to identify possible corrosion activity.
In addition, the measurement of pipe potential to its environment at regular intervals helps to identify the more corrosion-active areas. Accordingly, when a pipe is buried, electrolysis test stations or terminals will be established with leads being coupled from the underground detection points (pipe, sacrificial anode, electrolyte concentrate, etc.) to a ground level test station having terminals for direct voltage or current measurement. These measurements are manually taken by utility personnel at each test station location.
Gas, electric, telephone and water utilities have utilized such measurement techniques for many years as part of a cathodic protection program for detection or prevention of corrosion. Typically, such measurements are taken at a ground level test station which comprises a flat terminal board enclosed in a rigid, protective encasement. This casement is usually cylindrical in form, with a top cover to protect the terminal and attached leads from damage. These leads are coupled by conductive wire to various test points along the pipe length, as well as other sites of interest.
Several problems arise with the present types of test stations. Where the terminal encasement is below ground level, its location may be difficult to find. In urban areas, locations are typically mapped and are exposed on sidewalk or road surfaces. Except for problems arising from vandalism, such ground level test stations provide the desired protection and access for measuring current and voltage at underground pipes.
In a rural setting, however, underground pipelines traverse fields, open terrain, and other areas where vegetation, earth and other natural cover may conceal the test station location. It will be apparent that much of the underground pipeline of utilities spans distances between cities and even states and is subject to a variety of soil conditions which create the need for some form of cathodic protection.
In order to deal with the problem of identification and location of terminal test stations, above-ground terminals have been developed which are similarly constructed of an outer protective encasement which encloses the terminal and attached leads. Such aboveground test stations have a rigid cylindrical or tubular body, customarily fabricated from strong plastics, such as a glass-filled polycarbonate. These tubular structures are rigid, column-like structures which are intended to have a sufficiently high profile to be identifiable to maintenance personnel. This high profile, tubular structure follows the pattern of cylindrical encasements which have been used for many years in ground level test stations.
The above-ground test station is even more vulnerable to vandalism problems, however, than was its ground level counterpart. This is true because the structure is recognizeably distinct as a test station and represents a high profile target for destruction by vandals. In addition to losses from vandalism, damage to the tubular structure and contained terminal is frequently caused by roaming animals and farm equipment. For example, tractors and cross-country vehicles can quickly destroy such terminal stations upon impact.
Therefore, the industry is faced with the dilemma of choosing between low-risk ground level detection stations (which are very difficult to locate) or highly vulnerable above-ground test stations subject to damage from vandals, animals, and farm equipment. In view of the cost of labor and travel associated with locating a ground level system of test stations, this choice is usually biased in favor of the vulnerable above-ground devices as described. Accordingly, the utility industries and public must bear the cost of repeated replacement and repair of the above-ground terminal test station. The accepted strategy for minimizing test station damage appears to be to reinforce and strengthen the encasement to rigidly resist effects of damaging influences.
What is needed, therefore, is an improved cathodic protection or electrolysis test station (referred to hereafter as ETS) which as a high, visible profile suitable for easy identification, yet does not draw attention and is capable of surviving the impact or contact with vandals, vehicles, or roving animals.